An image sensor converts an optical image into an electrical signal. Types of image sensors include charge-coupled devices (CCDs) and complementary-metal-oxide-semiconductor (CMOS) image sensors. Image sensors are commonly used in digital cameras as well as other imaging devices.
Image sensors include pixels, which accumulate charge when illuminated by light. Conventionally, pixels accumulate a charge in an analog circuit for a continuous period of time referred to as an exposure time. The accumulated charge is transferred to an analog-to-digital (A/D) converter, which converts the accumulated charge into a digital value for that pixel. Conventionally, an image sensor outputs a two-dimensional (2D) array of digital values.